TY  - RPRT
TI  - SOME FUNCTION CLASSES CONNECTED WITH PARTIALLY HYPOELLIPTIC DIFFERENTIAL OPERATORS.
AU  - J Friberg
PY  - 1962
DO  - 10.1073/pnas.48.1.22-b
UR  - https://pubmed.ncbi.nlm.nih.gov/16590912/
ID  - 16590912
ER  -